In order to identify each of the cells that are managed by a base station in a cellular wireless communication system such as an LTE (Long Term Evolution) system, a Physical Cell Identity (PCI) is assigned to each cell (for example, refer to Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2013-021450)). A PCI is used for identifying cells at the time of, for example, performing handover that switches the cells to which a mobile station is connected. As a result, a PCI must be assigned to each cell to prevent the occurrence of PCI Collision in which the same PCI is assigned to a plurality of cells that are arranged in proximity.
In the following explanation, the operation of a base station according to a typical method of assigning PCI is described with reference to the sequence chart shown in FIG. 2 taking as an example a case in which cell #19 is newly arranged in a state in which a plurality of cells, to which PCI have been assigned (cells #1-#18), are arranged as shown in FIG. 1. In the following explanation, the base station that manages cell #19 is referred to as the newly-established base station, and the base stations that manage adjacent cells (cells #1-#6) that are adjacent to cell #19 are referred to as peripheral base stations.
The peripheral base stations acquire cell information that indicates the PCI assigned to the adjacent cells from base stations that manage the adjacent cells of the cells they manage (Step S11). For example, the base station that manages cell #6 acquires cell information from the base stations that manage cells #1, #5, #7, #17, and #18.
The peripheral base stations next, upon receiving an inquiry from the newly-established base station, regarding the adjacent cells of cell #19 create adjacent cell lists that indicate the PCI assigned to the adjacent cells based on the acquired cell information and supply the adjacent cell lists to the newly-established base station (Step S12).
The newly-established base station determines a candidate of the PCI that is intended to be assigned to cell #19 based on the adjacent cell lists (Step S13). Here, the newly-established base station determines a PCI other than the PCI indicated in the adjacent cell lists as the assignment candidate PCI. PCI (PCI #0-#17) that have been assigned cells that are adjacent to cell #19 (cells #1-#6) and the cells that are adjacent to these adjacent cells (cells #7-#18) are included in the adjacent cell lists that were acquired from the peripheral base stations. Accordingly, the newly-established base station determines, for example, PCI #18, that has not been assigned to cells #1-#18, as the assignment candidate PCI.
The newly-established base station then assigns PCI #18, that was determined as the assignment candidate, to cell #19 (Step S14) and supplies to the peripheral base stations a PCI assignment notification that indicates that PCI #18 has been assigned to cell #19 (Step S15).
By thus assigning a PCI, that is not contained in the adjacent cell lists acquired from the peripheral base stations, to the cell that is the object of assignment, the newly-established base station is able to prevent the occurrence of a PCI collision between cells that are adjacent to cell that is the object of assignment and the cells that are adjacent to these adjacent cells.
Although this explanation used an example in which cell #19 is newly arranged in FIG. 1 and FIG. 2, the base station that changes the PCI of cell #19 (hereinbelow referred to as the “altering base station”) is also able to change the PCI by the using same process as that of the newly-established base station shown in FIG. 2 in a case in which cell #19 has already been arranged and the PCI of cell #19 is to be changed.